Cements, Pozzolans and Blends

Halliburton provides different classifications of cement from cement manufacturers based on downhole conditions of a specific area. The American Petroleum Institute sets forth specifications for the manufacture of cement in API Specification 10A, Twenty-first Edition, September 1, 1991.

The base cement is usually modified with blended additives or liquid additives so the properties of the cement slurry are suitable for the various types of formations encountered in a well.

Portland cement can be extended with pozzolanic material to yield an economical slurry with premium properties. Combining pozzolanic material with cement produces a reaction that can improve the properties and compressive strength of the set cement sheath.

Cements, Pozzolans and Blends

When drilling through several very weak zones in Oldham County, Texas, an operator was having to use drilling fluids with density just above that of water in order to avoid lost circulation issues.
In fact, the production casing traversed some of the weakest zones. Thus, the slurry density needed to be light enough to avoid fracturing the formation, while retaining mechanical properties of a cement sheath to resiliently withstand the forces of fracture stimulation and production cycling and maintain zonal isolation integrity throughout the life of the well.

A Permian Basin operator completed a new injection well and placed it on injection when field personnel noticed an area of continuously wet ground surrounding an offset water source well, about 150 ft from the new well. Several attempts to squeeze off the flow were unsuccessful. Log interpretation indicated the water entered the new well just below 2,800 ft, exited and re-entered the casing annulus, exited the new well at about 300 ft and surfaced around the offset source water well. Eventually, the invading water moved toward two other offset production wells located on the lease. Testing determined the water invasion traveled to the new well from an offset injection well on an adjacent property via either a natural or induced fracture network.
Halliburton's Solution

Typically, the wells are cemented with a high quality cement covering two formations to a depth above a corrosive formation. Specifications
varied among the wells and included 9,500 to 11,000 ft depth, 2 7/8-in
casing in 7 7/8-in hole, 4 1/2-in casing in 7 7/8-in hole, dual 2 7/8-in
casing in 7 7/8-in hole, and dual 4 1/2-in casing in 9 5/8-in hole. Temperature ranged from 160F at the top to 265F at TD.

A major operator's wells located offshore Alabama were exhibiting high pressures in the intermediate liner/tieback annulus after going through a production cycle. Pressures were high enough to cause casing failures and fracture the adjacent cement sheath. Conventional approaches to solving the problem failed to control the annular pressure buildup. Well specifications include TVD 16,850 ft, BHST 300F, and a 9 -in liner.
Halliburton's Solution

An east Texas turnkey drilling contractor was drilling a new hole below a 9 5/8-in casing shoe just below 16,000 ft when mud weight had to be increased to handle gas flow. A sand zone about 75 ft below the shoe then began to take the mud. The maximum mud weight for the sand
was measured at 16.5 lbs/gal, which was insufficient to reach the planned
well depth. The initial leakoff measured at the 2 3/8-in casing point
was 17.2 lbs/gal equivalent mud weight. The drilling contractor needed
a way to prevent the need to set a 7 5/8-in drilling liner and a way to
minimize the impact on the drilling curve.
Halliburton Solution follows --

A Permian Basin operator with a continuous drilling program needed to reduce cementing costs and wanted to review the current system for possible cost savings. One area of emphasis was surface pipe cementing. Nearly every job required a top-out job before drilling could continue. This not only required extra cement and pumping, but it also increased the rig time and required additional temperature surveys. Typical well specifications included: casing setting depth of 2,000 ft, casing size of 8 in, and hole size of 11 in.